Senior metalworker losing weight (5)
I believe the answer is:
elder
'senior' is the definition.
(I know that senior can be written as elder)
'metalworker losing weight' is the wordplay.
'metalworker' becomes 'welder' (I've seen this in another clue).
'losing' is a deletion indicator.
'weight' becomes 'w' (short for weight).
'welder' with 'w' taken out is 'ELDER'.
(Other definitions for elder that I've seen before include "Berry-bearing shrub" , "Senior churchperson" , "Older person - one's senior" , "Senior type of tree?" , "Tie up" .)