Hi sab, First of all, did you mean "'첫사랑'이라는 한단어(one word that is called 'a first love'')" or "'첫사랑에'라는 한단어(one word that is called 'to a first love'')"? I think you meant the first but I will just explain both. 1) '첫사랑'이라는 한단어가 표현할 수 있는데요. =the one word "a first love" can express it. Ex. 당신이 민호씨를 볼때 느끼는 감정은 '첫사랑'이라는 한단어가 표현할 수 있는데요. =the one word 'a first love' can express the feeling you have when looking at Min-ho. 2) '첫사랑에'라는 한단어가 표현할 수 있는데요. =the one word(phrase) 'to a first love' can express it. Ex. 그 시의 주제는 시에 나온 '첫사랑에'라는 한단어가 표현할 수 있는데요. =the one word 'to a first love' in the poem can express the subject of the poem. FYI, '~는데요' format is used when the sentence is followed by another sentence. Ex. 당신이 민호씨를 볼때 느끼는 감정은 '첫사랑'이라는 한단어가 표현할 수 있는데요. 첫사랑은 인생에 딱 한번만 옵니다. 그러니까 민호씨를 쉽게 보내주지 마세요. =the one word 'a first love' can express the feeling you have when looking at Min-ho. (And) first love comes only once in life. So do not let him go easily. Additionally "Being in a first love that can be expressed with one word" can be translated as "한단어로 표현될 수 있는 첫사랑에 빠진다는 것". '한단어' in the above examples were referring to '첫사랑' but '한단어' in this sentence means literally '한단어'(one word). Hope it helps,

Can you give some of the context please?