This post is to put to rest a ghost of mine. When I went to University I thought lots of the words I used daily were standard English (why would I think anything else!?) and was a little surprised when others from around the UK were bemused when I used them.
SPELK is a great word and is only ever used to mean a splinter (of wood), generally in the finger. Upon meeting Scandinavian or Dutch people I would always corner them and ask what 'splinter' was in their language and, until now, I've had no luck and thought spelk was an isolated Northern word, unrelated to other Germanic languages.
Tonight I found the answer here!
It states that spelk comes from Old English (spelc or spilc) for splints (surgical supports). Also related to Old Norse spelkur (splints).
Splint (still in the sense of surgical support) in different languages:
This page here refers directly to the NE dialect word 'spelk' in the first paragraph:
"oe. spelc ‘spalk’ (ne. dial. spelk)"
The same source states that spelk, spelc, spalk all derive from the word 'to split' (that is to say "cleave piece of wood):
"Het woord betekent eigenlijk ‘afgespleten stuk hout’ en is een afleiding van de wortel 'splijten'"