hart's tonguePronunciation: /ˈhɑːtstʌŋ/ (also hart's tongue fern)Definition of hart's tongue noun a common European fern whose long, narrow undivided fronds are said to resemble the tongues of deer. Phyllitis (or Asplenium) scolopendrium, family Aspleniaceae hart's tongue in other Oxford dictionaries Definition of hart's tongue in the US English dictionary