Entries linking to fill-in
Old English fyllan "to fill, make full, fill up, replenish, satisfy; complete, fulfill," from Proto-Germanic *fulljanan "to fill" (source also of Old Saxon fulljan, Old Norse fylla, Old Frisian fella, Dutch vullen, German füllen, Gothic fulljan "to fill, make full"), a derivative of adjective *fullaz "full" (see full (adj.)). Related: Filled.
To fill the bill (1882) originally was U.S. theatrical slang, in reference to a star of such magnitude his or her name would be the only one on a show's poster. To fill out "write in required matter" is recorded from 1880.
a Middle English merger of Old English in (prep.) "in, into, upon, on, at, among; about, during;" and Old English inne (adv.) "within, inside," from Proto-Germanic *in (source also of Old Frisian, Dutch, German, Gothic in, Old Norse i), from PIE root *en "in." The simpler form took on both senses in Middle English.
Sense distinction between in and on is from later Middle English, and nuances in use of in and at still distinguish British and American English (in school/at school). Sometimes in Middle English shortened to i.
The noun sense of "influence, access (to power or authorities)," as in have an in with, is first recorded 1929 in American English. to be in for it "certain to meet with something unpleasant" is from 1690s. To be in with "on friendly terms with" is from 1670s. Ins and outs "intricacies, complications of an action or course" is from 1660s. In-and-out (n.) "copulation" is attested from 1610s.