<span class="searchmatch">bùird</span>-<span class="searchmatch">dhuibh</span> genitive singular of bòrd-dubh...
bòrd (“board”) + dubh (“black”); calque of English blackboard bòrd-dubh m (genitive singular <span class="searchmatch">bùird</span>-<span class="searchmatch">dhuibh</span>, plural <span class="searchmatch">bùird</span>-dhubha) blackboard...