homolog (homologue; homologous; homologous series)

A compound belonging to a series of compounds that differ by a repeating group. For example, propanol (CH3CH2CH2OH), n-butanol (CH3CH2CH2CH2OH), and n-pentanol (CH3CH2CH2CH2CH2OH) are homologs; they belong to a homologous series CH3(CH2)nOH.