I wwas told to write a 3 syllable word for each clue. The first letter is provided.

1.Rational or reasonable [Clue:L}
2.To stand for or symbolise {clue:R]

2 answers

2 is represent. I don't know about 1. You should look it up in a thesaurus to find synonyms.

www.thesaurus.com
It is plausible that you might find an answer for number one.