Answer
Definition: A carbonyl group with one alkyl group and one hydrogen.
Example: Ethanal (acetaldehyde) $CH_3CHO$
Work Step by Step
Definition: The carbonyl group, C=O, is the functional group for both aldehydes and ketones. An aldehyde has one alkyl group and a hydrogen atom bonded to the carbonyl group. General formula RCHO.
Example: Ethanal (acetaldehyde) $CH_3CHO$