Second - skund

1) skund
The shortest possible Icelandic name for second is 'skund'. The words scores on many fronts.
1) It is short
2) It sounds like the international word and Icelandic 'stund' and is declined like the latter word.
3) It refers to the verb "skunda" (hurry). Indeed, a "second" is the time-frame often refered to when someone is in a hurry.

2) Other possibilities:
tifskeið or tifstund (tick-period), stundarkorn (hour-particle, moment)