Lewis & Short

quĕrŭlus, a, um, adj. [queror].

  1. I. Lit., full of complaints, complaining, querulous (mostly poet.; not in Cic.): (senex) difficilis, querulus, laudator temporis acti, Hor. A. P. 173: ululatus, Ov. H. 5, 73: dolor, id. Tr. 3, 8, 32: vox, id. A. A. 2, 308: fastus, Mart. 12, 75, 7: calamitas, Curt. 5, 5, 12: libelli rusticorum, Plin. Ep. 9, 15, 1: nec querulus essem, id. Pan. 4, 9, 21.
  2. II. Poet., transf., of animals and things, softly complaining, uttering a plaintive sound, murmuring, cooing, warbling, chirping, etc.: querulae cicadae, Verg. G. 3, 328; cf.: nidus volucrum, Ov. Med. Fac. 77: rana, Col. 10, 12: capella, Mart. 7, 31, 3: fetus suis, Petr. 133: chorda, Ov. Am. 2, 4, 27: tibia, Hor. C. 3, 7, 30: tuba, Prop. 4 (5), 3, 20.