Etymology: Appears first about 1600. In sense 1, it answers to Latin complēre to fill up, fulfil, accomplish, complete v. This verb became in Romanic complīre , whence Italian compire , compiere , Provençal complir , Old French complir (see complish v.), all in the original sense. But in Old Catalan complir or Spanish cumplir , the sense underwent the development ‘to fill up, make up what is wanting, satisfy, satisfy the requirements or forms of courtesy’ = comply with , in sense 2 below. In this latter sense, complire appears to have been adopted in 16th cent. Italian, by the side of the native compire in the original sense; and the Italian was evidently the immediate source of sense 2 (In the same way the Old Catalan or Spanish form and sense of the derivative noun complimento , complimiento , was the source of Italian complimento , and so of the 16th cent. French compliment , and 17th cent. English compliment n.) As to the form of comply compare supply v.¹ (Latin supplēre , Italian supplire , Old French soupleyer (15th cent. suppleyer , suppléer ), late Middle English sowplé , 15th cent. supple , supplie , supply . On the model of this, and with the same relation of form to Latin complēre , Italian complire , that supply bore to supplēre , supplire , but without the same antecedent history, comply appears to have come into use in the end of the 16th cent. (Old French complir was by that time obsolete.) In the sense-development in English there has been a tendency to association with ply v.¹, French plier , Latin plicāre to bend, so as to make ‘bending to the will of another’ a more prominent part of the notion: compare especially compliant adj.

Etymology: apparently < Latin complicāre; compare apply v., representing Latin applicāre, etc.