Back issues of Linux User magazine belong primarily in the past (7)
I believe the answer is:
lumbago
'back issues' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'linux user magazine belong primarily in the past' is the wordplay.
'primarily' suggests taking the first letters.
'in the past' becomes 'ago' (three years ago means three years in the past).
The first letters of 'linux user magazine belong' is 'lumb'.
'lumb'+'ago'='LUMBAGO'
'of' is the link.
Can you help me to learn more?
(Other definitions for lumbago that I've seen before include "Form of backache" , "Rheumatic pain in the small of the back" , "Maul bog badly for a rheumatic affliction" , "Rheumatism of lower back" , "Back complaint" .)