Appeal for help by old pedestrian (2-2)
I believe the answer is:
so-so
'pedestrian' is the definition.
(both can mean dull or mediocre)
'appeal for help by old' is the wordplay.
'appeal for help' becomes 'sos' (I've seen this in another clue).
'by' is a charade indicator (letters next to each other).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'sos'+'o'='SO-SO'
(Other definitions for so-so that I've seen before include "Mediocre" , "Of middling quality" , "Of average quality" , "Informally, only moderately good or well" , "Barely passable" .)