YOU SAID:

Weather is a boring subject

INTO JAPANESE

天気は話題として退屈です

BACK INTO ENGLISH

Weather is dull as the topic

INTO JAPANESE

天気は話題として鈍い

BACK INTO ENGLISH

The weather was dull as the topic

INTO JAPANESE

天気は話題として退屈だった

BACK INTO ENGLISH

The weather was dull as the topic