highlighter
US /ˈhaɪˌlaɪ.t̬ɚ/
UK /ˈhaɪˌlaɪ.t̬ɚ/

1.
a felt-tip pen with transparent, fluorescent ink, used for marking important passages in a text
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She used a yellow highlighter to mark the key points in her textbook.
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Make sure to bring your highlighter for the study session.
2.
a cosmetic product used to give a luminous glow to certain areas of the face
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She applied highlighter to her cheekbones for a radiant look.
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A good highlighter can really enhance your features.