sap

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A covered trench or tunnel dug to a point near or within an enemy position.
• intransitive verb To undermine the foundations of (a fortification).
• intransitive verb To dig a sap.
• noun A leather-covered bludgeon with a short, flexible shaft or strap, used as a hand weapon.
• transitive verb To hit or knock out with a sap.
• noun The watery fluid that circulates through a plant, carrying food and other substances to the various tissues.
• noun Health and energy; vitality.
• noun Slang A foolish or gullible person.
• transitive verb To drain (a tree, for example) of sap.
• transitive verb To deplete or weaken gradually: synonym: deplete.

from The Century Dictionary.

• noun The juice or fluid which circulates in all plants, being as indispensable to vegetable life as is the blood to animal life.
• noun Hence The juice or fluid the presence of which in anything is characteristic of a healthy, fresh, or vigorous condition; blood.
• noun The alburnum of a tree; the exterior part of the wood, next to the bark; sap-wood.
• To act like a sap; play the part of a ninny or a soft fellow.
• To undermine; render unstable by digging into or eating away the foundations, or, figuratively, by some analogous insidious or invisible process; impair the stability of, by insidious means: as, to sap a wall; to sap a person's constitution, or the morals of a community.
• Milit., to approach or pierce with saps or trenches.
• To dig or use saps or trenches; hence, to impair stability by insidious means.
• noun In archery, the light-colored portion of a bowstaff composed of the sap-wood. This portion forms the back of a self-bow.
• noun A quarryman's name for rock which is partially decayed and which exhibits this quality by iron stains and other discolorations. It is usually thrown away.
• noun Same as saphead.
• noun A tool for digging; a mattock.
• noun [⟨ sap, verb] Milit., a narrow ditch or trench by which approach is made to a fortress or besieged place when within range of fire.

from the GNU version of the Collaborative International Dictionary of English.

• intransitive verb To proceed by mining, or by secretly undermining; to execute saps.
• transitive verb To subvert by digging or wearing away; to mine; to undermine; to destroy the foundation of.
• transitive verb (Mil.) To pierce with saps.
• transitive verb To make unstable or infirm; to unsettle; to weaken.
• noun (Mil.) A narrow ditch or trench made from the foremost parallel toward the glacis or covert way of a besieged place by digging under cover of gabions, etc.
• noun (Mil.) a fascine about three feet long, used in sapping, to close the crevices between the gabions before the parapet is made.
• noun (Mil.) a large gabion, six or seven feet long, filled with fascines, which the sapper sometimes rolls along before him for protection from the fire of an enemy.
• noun The juice of plants of any kind, especially the ascending and descending juices or circulating fluid essential to nutrition.
• noun The sapwood, or alburnum, of a tree.
• noun Slang A simpleton; a saphead; a milksop.
• noun (Bot.) any large fungus of the genus Polyporus. See Polyporus.
• noun a dull light green pigment prepared from the juice of the ripe berries of the Rhamnus catharticus, or buckthorn. It is used especially by water-color artists.
• noun the dry rot. See under Dry.
• noun (Zoöl.) any one of several species of small American woodpeckers of the genus Sphyrapicus, especially the yellow-bellied woodpecker (S. varius) of the Eastern United States. They are so named because they puncture the bark of trees and feed upon the sap. The name is loosely applied to other woodpeckers.
• noun (Bot.) a vessel that conveys sap.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun uncountable The juice of plants of any kind, especially the ascending and descending juices or circulating fluid essential to nutrition.
• noun uncountable The sap-wood, or alburnum, of a tree.
• noun slang, countable A simpleton; a saphead; a milksop; a naive person.
• noun countable, US, slang A short wooden club; a leather-covered hand weapon; a blackjack.
• verb transitive, slang To strike with a sap (with a blackjack).
• noun military A narrow ditch or trench made from the foremost parallel toward the glacis or covert way of a besieged place by digging under cover of gabions, etc.
• verb transitive To subvert by digging or wearing away; to mine; to undermine; to destroy the foundation of.
• verb transitive, military To pierce with saps.
• verb To make unstable or infirm; to unsettle; to weaken.
• verb transitive To gradually weaken.
• verb intransitive To proceed by mining, or by secretly undermining; to execute saps — 12