Denshi Jisho — Online Japanese dictionary

頑張る がんばる 1: to persevere; to persist; to keep at it; to hang on; to hold out; to do one's best;
2: to insist that; to stick to (one's opinion);
3: to remain in a place; to stick to one's post; to refuse to budge
Common word, Ateji (phonetic) reading, Godan verb with ru ending, Intransitive verb 

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