embryo

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. An organism in its early stages of development, especially before it has reached a distinctively recognizable form.
2. n. An organism at any time before full development, birth, or hatching.
3. n. The fertilized egg of a vertebrate animal following cleavage.
4. n. In humans, the prefetal product of conception from implantation through the eighth week of development.
5. n. Botany The minute, rudimentary plant contained within a seed or an archegonium.
6. n. A rudimentary or beginning stage: "To its founding fathers, the European [Economic] Community was the embryo of the United States of Europe” ( Economist).

Century Dictionary and Cyclopedia

1. n. The fecundated germ of an animal in its earlier stages of development, and before it has assumed the distinctive form and structure of the parent; a germ; a rudiment; in a more extended sense, a rudimentary animal during its whole antenatal existance. In the later stages of development, especially in man and the mammals generally, the name fetus commonly takes the place of embryology In the cases of oviparous animals, the term embryo properly covers the whole course of development of the fecundated germ in the egg (which see, and see cut under dorsal): as, the hen's egg contained an embryo ready to hatch. By a late and loose, though now common, extension of the term, it is applied to various larval stages of some in vertebrates, which in the course of their transformation are frequently so different from the parent as to be described as distinct species or genera: as, the embryo (first larval stage) of a cestoid worm.
2. n. In botany, the rudimentary plant contained in the seed, the result of the action of pollen upon the ovule. It may be so rudimentary as to have apparently no distinction of parts; but even in its simplest form it consists virtually of a single internode of an axis, which upon germination develops at one extremity a leaf or leaves with a terminal bud, and a root at the other. In more developed embryos this initial internode or caulicle (often incorrectly called radicle) bears at one end one, two, or more rudimentary leaves called cotyledons, and often an initial bud or plumnle. Also called germ. By recent authors the term is also applied to the developed oöspore in vascular cryptogams. See cuts under albumen and cotyledon.
3. n. The beginning or first state of anything, while yet in a rude and undeveloped condition; the condition of anything which has been conceived but is not yet developed or executed; rudimentary state: chiefly in the phrase in embryo.
4. n. Synonyms Fetus, Germ, Rudiment. The first of these words is mainly applied to the embryos of viviparous vertebrates in the later stages of their development, when they are more subject to observation. Germ means especially the seed or fecundated ovum, and scarcely extends beyond the early stages of an embryo. Rudiment is simply the specific application of a more general term to a germ or to the early, crude, or ‘rude’ stages of an embryo.
5. Being in the first or rudimentary stage of growth or development; incipient; embryonic: as, an embryo flower.

Wiktionary

1. n. In the reproductive cycle, the stage after the fertilization of the egg that precedes the development into a fetus.
2. n. An organism in the earlier stages of development before it emerges from the egg, or before metamorphosis.
3. n. In viviparous animals, the young animal's earliest stages in the mother's body
4. n. In humans, usually the cell growth up to the end of the seventh week in the mother's body
5. n. botany A rudimentary plant contained in the seed.
6. n. The beginning; the first stage of anything.

GNU Webster's 1913

1. n. The young of an animal in the womb, or more specifically, before its parts are developed and it becomes a fetus (see fetus).
2. n. The germ of the plant, which is inclosed in the seed and which is developed by germination.
3. adj. Pertaining to an embryo; rudimentary; undeveloped.

WordNet 3.0

1. n. an animal organism in the early stages of growth and differentiation that in higher forms merge into fetal stages but in lower forms terminate in commencement of larval life
2. n. (botany) a minute rudimentary plant contained within a seed or an archegonium