Hungarian Historical Phonology oson
oson 'sneak'
First attestation/Old Hungarian data
First attested in the 18th century (see UEW)
Important dialectal forms
ossan (Gyula), ussan (Jászság), ussan (Óbást) (ÚMTSz: IV: 213, s.v. oson)
Uralic/Ugric/Pre-Hungarian reconstruction
[coming]
Loan etymology
None suggested
Cognates suggested in earlier research
See the cognates listed by UEW (note that the Uralic background of the Hungarian word is not accepted in this source)
Commentary
It is noted in the UEW that the Hungarian verb oson 'sneak (schleichen)' has been connected to Uralic *aćka- 'step' in the past (UEW reconstructs *aśke-, but the Uralic verb was an *a stem, see Zhivlov 2014: 129). UEW rejects the comparison due to various reasons: Hungarian o does not point to Uralic *a; the semantic connection is problematic; and the word oson is attested late, only in the end of the 18th century.
However, Helimski, in his unfinished Marginalia ad UEW manuscript, supports the Uralic etymology of oson, noting that the are cases of Proto-Uralic/Finno-Ugric *a being reflected by Hungarian o. The example Helimski mentiongs, Hungarian orvos < PFU *arpa can hardly be correct, but Hungarian fos from Uralic *paćka seems to be a good parallel. In both these etymologies, *a > o has taken place before Proto-Uralic *ć(k).
The semantic argument of the UEW is not that strong, as a meaning 'move cautiously' could probably be derived from a more general meaning 'step'.
The last argument presented in the UEW, the late attestation, admittedly makes the Uralic etymology suspicious. However, a late attestation does not automatically rule a Uralic etymology out.
Conclusion
The Proto-Uralic origin does not involve phonological problems but the late attestation of the Hungarian word remains somewhat problematic.
References
Helimski: Marginalia ad UEW: PU
UEW s.v. aśke (aśke-lɜ), aćke (aćke-lɜ): not PU Uralonet