This is the 247th most frequent Thai word.
เมษ
"เมษ" means "Aries" or relates to the month of April in Thai.
In this sentence, "เมษา" is part of the Thai shorthand for "April," taken from the word "เดือนเมษายน," which means "the month of April."
เดือนที่ร้อนที่สุดของปีในประเทศไทยคือเดือนเมษา
The hottest month of the year in Thailand is April.
Here, "เมษ" is used to refer to the astrological sign Aries in Thai.
เขาเกิดในราศีเมษ
He was born under the zodiac sign of Aries.
Similarly, "เมษา" in this context refers to the month of April in a poetic or colloquial form.