from The American Heritage® Dictionary of the English Language, 4th Edition
- n. An entry, such as one in an account, catalog, or reference work, that is included within a main entry.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A subordinate entry
from The Century Dictionary and Cyclopedia
- n. A subordinate entry; an entry made under another.
Sorry, no etymologies found.
The subentry for the phrase in concert (with) starts with an early 18th century citation:
I think the best tool is probably a simple spreadsheet or database, where you can list entry, potential subentry, and page number.
That is not the case for alternating current, a subentry under alternate, or the array to be found under pass, which includes in passing (participle/gerund), make a pass at (noun), pass by (verb), passed pawn (adjective/past participle).