Thanks for spotting!
No, it’s an error. The word definately exists in the dictionaries:
32413: “word”: “nīvaraṇa”,
32414: “text”: “
neuter, occasionally masculine an obstacle, hindrance, only as tt. applied to obstacles in an ethical sense & usually enumerated or referred to in a set of 5 (as pañca nīvaraṇāni and p. āvaraṇāni), viz. kāmacchanda, (abhijjhā-)vyāpāda, thīna-middha, uddhaccakukkucca vicikicchā i.e. sensuality, ill-will, torpor of mind or body, worry, wavering (cp. Dhs. trsl. p. 310) DN.i.73 (˚e, acc. pl.), DN.i.246; DN.ii.83, DN.ii.300; DN.iii.49 sq., DN.iii.101, DN.iii.234, DN.iii.278; SN.ii.23; SN.iii.149; SN.v.60, SN.v.84 sq., SN.v.93 sq., SN.v.145, SN.v.160, SN.v.226 SN.v.327, SN.v.439; MN.i.60, MN.i.144, MN.i.276; MN.iii.4, MN.iii.295; AN.i.3, AN.i.161 AN.iii.16, AN.iii.63, AN.iii.230 sq.; AN.iii.386; AN.iv.457; AN.v.16, AN.v.195, AN.v.322; Snp.17 Mnd.13; Cnd.379; Pts.i.31, Pts.i.129, Pts.i.163; Pp.68; Dhs.1059 Dhs.1136, Dhs.1495; Vb.199, Vb.244, Vb.378; Ne.11, Ne.13, Ne.94; Vism.146, Vism.189; DN-a.i.213; Sdhp.459, Sdhp.493 and passim. Other enumns are occasionally found e.g. 10 at SN.v.110 SN.v.8 at MN.i.360 sq.; MN.i.6 at Dhs.1152.
Sk. *nivāraṇa, nis + varaṇa of vṛ; (vṛṇoti), see nibbuta & cp. nivāraṇa
The lookup tool works fine with this word.
I’ve made a ticket for it: