This root form (lemma) is used in 2 different forms in the NT: φοβερὰ (NFS), φοβερὸν (NNS).
It is glossed in 2 different ways: ‘a fearful thing’, ‘fearful’.
OET HEB 10:27 Greek word=φοβερὰ (fobera) Morphology=NFS English gloss=‘fearful’ SR GNT HEB 10:27 word 1
OET HEB 10:31 Greek word=φοβερὸν (foberon) Morphology=NNS English gloss=‘a fearful thing’ SR GNT HEB 10:31 word 1
OET HEB 12:21 Greek word=φοβερὸν (foberon) Morphology=NNS English gloss=‘fearful’ SR GNT HEB 12:21 word 3