WikiRhymer has about 6,000 rhyming words and phrases for "smarter" starting with...

arter
    barter
      carter
        charter
          darter
            garter
              martyr
                starter
                  nonstarter
                    Karter
                      Sartor
                        Tartar
                          Tarter
                            Pure Rhyme Set #1 of 1 (Add to/Edit Set Members)
                            Words that have a pure rhyme on their last syllable only.
                            partner
                              Gartner
                                End Rhyme Set #1 of 619 (Add to/Edit Set Members)
                                Arthur
                                  MacArthur
                                    McArthur
                                      End Rhyme Set #2 of 619 (Add to/Edit Set Members)
                                      armer
                                        armor
                                          armour
                                            charmer
                                              farmer
                                                Harmer
                                                  Marmor
                                                    • knight in shining armour
                                                    End Rhyme Set #3 of 619 (Add to/Edit Set Members)

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                                                    Words that "almost" rhyme on the vowel-based rhyme sound of the stressed syllable like: be/eat or maybe/shapely. (Click for more info)
                                                    partner
                                                      Gartner
                                                        Near Rhyme Set #1 of 62 (Add to/Edit Set Members)
                                                        Arthur
                                                          MacArthur
                                                            McArthur
                                                              Near Rhyme Set #2 of 62 (Add to/Edit Set Members)
                                                              armer
                                                                armor
                                                                  armour
                                                                    charmer
                                                                      farmer
                                                                        Harmer
                                                                          Marmor
                                                                            • knight in shining armour
                                                                            Near Rhyme Set #3 of 62 (Add to/Edit Set Members)

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                                                                            Rhymes made up of more than one word. For instance, "jealous" and "tell us" or "shaky" and "make me."

                                                                            We have no mosaic rhymes for "smarter".

                                                                            Mosaic Rhyme Set #1 of 1 (Add to/Edit Set Members)