Source : WordNet®

soft spot
     n 1: a place of especial vulnerability [syn: {weak part}, {weak
          spot}] [ant: {good part}]
     2: a sentimental affection; "she had a soft spot for her
        youngest son"
     3: any membranous gap between the bones of the cranium in an
        infant or fetus [syn: {fontanelle}, {fontanel}]