Relating to or constituting a compliment; expressing praise or flattery.
From compliment plus the adjective-forming suffix -al (from Latin -alis). This formation creates an adjective meaning 'of the nature of a compliment.'
English speakers almost never use 'complimental'—we say 'complimentary' instead, which is shorter and has become the standard. This shows how words compete within categories and how arbitrary the winners often are: both are equally logical, but one survives through frequency.
Complete word intelligence in one call. Free tier — 50 lookups/day.