Wiktionary
pre. (context organic chemistry English) Used to form classification names for classes of organic compounds which contain a carbon skeleton but no aromatic rings. See e.g. alkyl, alkane.
Wikipedia
Usage examples of "alk-".
I moved to the L-shaped counter, where a uniformed officer monitored the walk-in trade.
On the far wall, two doors stood open, one leading to a small bathroom, the other into what was clearly a spacious walk-in closet.
At one end of the room, double doors stood open to reveal a large walk-in closet the size of my loft.
Fiona had been moving back and forth from the bed to the walk-in closet, carrying blouses and skirts, which she hung on matching white satin-padded hangers.
For instance, under the entry ÁLAK (LR:348), itself defined "rushing", we find this series: "*alk-w&UnknownEntity.
In the sources, macrons are normally used instead: We have already quoted alk-w&UnknownEntity.
There were rooms beyond that one, small corridors that twisted back on themselves, even a walk-in closet that had been made to house a Hunt Shoppe display.
There was a conveyor strip for possessions beside the walk-through entrance, but he held on to the bag.