Wordnet 3.0
NOUN (1)
1.
an ache localized in the back;
The Collaborative International Dictionary of English v.0.48:
backache \back"ache\ n.
an ache localized in the back.
[WordNet 1.5]
WordNet (r) 3.0 (2006):
backache
n 1: an ache localized in the back