相互
xiānghù · HSK 3
each other
🔄 相 = mutual/each-other + 互 = reciprocal; doubled-up word for 'mutually'
相 alone already means 'each other' (as in 相同 same-as-each-other); 互 means 'reciprocal/alternating' (as in 互联网 inter-net). Stacking them gives an emphatic 'mutually, one another'.