Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ancillor, ātus, 1, v. dep. and n. [ancilla], pr., to serve as handmaid; hence, in gen., to serve, to attend upon, to be subservient to, etc. (only ante-class. and post-Aug.): invita ancillans, Att. ap. Non. p. 72, 3: uxoribus ancillantur, Titin. ib.: aestus (maris) ancillantes siderum avido trahenti etc., Plin. 2, 97, 99, § 213: cetera membra ancillari et subservire capiti, App. Dogm. Plat. 1, p. 9, 17.