Old English fullfyllan "fill up" (a room, a ship, etc.), "make full; take the place of (something)," from full (adj.), here perhaps with a sense of "completion" + fyllan (see fill (v.), which is ultimately from the same root).
It was used from mid-13c. in reference to prophecy (probably translating Latin implere, adimplere). From mid-13c. as "do, perform; carry out, consummate, carry into effect;" from c. 1300 as "complete, finish; satiate, satisfy, gratify." Related: Fulfilled; fulfilling.
Modern English combinations with full tend to have it at the end of the word (as -ful), but this is a recent development and in Old English it was more common at the start, but this word and fulsome appear to be the only survivors.
Self-fulfilling prophecy is attested by 1949, associated with and popularized by U.S. sociologist Robert K. Merton, in writings on racial prejudices, who described it as a false definition of a situation at the outset that evokes a behavior which seems to validate the false concept.
Middle English folwen, from Old English folgian, fylgian, fylgan "to accompany (especially as a disciple), move in the same direction as; follow after, pursue, move behind in the same direction," also "obey (a rule or law), conform to, act in accordance with; apply oneself to (a practice, trade, or calling)," from Proto-Germanic *fulgojanan (source also of Old Saxon folgon, Old Frisian folgia, Middle Dutch volghen, Dutch volgen, Old High German folgen, German folgen, Old Norse fylgja "to follow"). Probably originally a compound, *full-gan, with a sense of "full-going," the sense then shifting to "serve, go with as an attendant" (compare fulfill). Related: Followed; following.
Sense of "accept as leader or guide, obey or be subservient to" was in late Old English. Meaning "come after in time" is from c. 1200; meaning "to result from" (as effect from cause) is from c. 1200. Meaning "to keep up with mentally, comprehend" is from 1690s. Intransitive sense "come or go behind" is from mid-13c. To follow one's nose "go straight on" first attested 1590s. "The full phrase is, 'Follow your nose, and you are sure to go straight.' " [Farmer]. The children's game follow my leader is attested by that name from 1812 (as follow the leader by 1896).
late 14c., "fulfill, perform, carry out an undertaking," from Old French acompliss-, present-participle stem of acomplir "to fulfill, fill up, complete" (12c., Modern French accomplir), from Vulgar Latin *accomplere, from Latin ad "to" (see ad-) + complere "to fill up," transferred to "fulfill, finish (a task)," from com-, here probably as an intensive prefix (see com-), + plere "to fill" (from PIE root *pele- (1) "to fill"). Related: Accomplished; accomplishing.
late 14c., "make complete, bring to an end, supply what is lacking; fulfill, accomplish," from complete (adj.) and probably in part from Latin completus. Related: Completed; completing.
c. 1200, "willing to serve (someone); willing to fulfill an obligation," from Old French obedient "obedient" (11c.), from Latin oboedientem (nominative oboediens) "obedient, compliant," present participle of oboedire "to obey" (see obey).
early 14c., "to carry out, fulfill" (transitive), probably from Old French compli, past participle of complir "to accomplish, fulfill, carry out," from Vulgar Latin *complire, from Latin complere "to fill up," transferred to "fulfill, finish (a task)," from com-, here probably as an intensive prefix (see com-), + plere "to fill" (from PIE root *pele- (1) "to fill").
Intransitive sense of "to consent, act in accordance with another's will or desire" is attested from c. 1600 and might have been influenced by ply (v.2), or perhaps it is a reintroduction from Italian, where complire had come to mean "satisfy by 'filling up' the forms of courtesy" (compare compliment (n.)).