-al definition

From adjective suffix , or French .

of or pertaining to; adjectival suffix appended to various words, often nouns, to make an adjective form. Often added to words of Latin origin, but used with other words also.

line, lineal

base, basal

cranium, cranial
Forming nouns, especially of verbal action.

e.g. rival, proposal, denial
the IUPAC nomenclature used in organic chemistry to form names of aldehydes containing the -(CO)H group. It was extracted from the word "aldehyde".

If the root word ends in l, the variant -ar is often used instead. Sometimes both forms are found: linear, lineal.