When Hangeul was first invented, it was named 'Hunminjeongeum(훈민정음)' by King Sejong. It means "The
true sound(letters) to be used to teach people".
However, the noble people at that time did not welcome the
advent of Hangeul, and since they were imbued with the view
that China is the center of the world, they kept an attitude
of despising Hangeul compared to Chinese characters and writings.
Therefore, Chinese characters and writings were called 'Jinseo(진서)-meaning
true letters' whereas Hangeul was often called 'Eonmun(언문)'
And there are some views that Hangeul was called
'Amkul(암클)' because it was mainly used by
women, or 'Ahatkul(아했글)' because it was only for the use of
children who did not learn Chinese characters. However,
we cannot confirm whether the names were actually used because
there is no clear record of use of the names 'Amkul' or 'Ahatkul'.
During the civilization period, names like 'Jeongeum(정음)',
'Gungmun(국문)' were often used due to the high valuation
of Hangeul, letters native to Korea, as people began to cherish
national spirit. Ju Si-gyeong seems to be the first who named
Korean letters 'Hangeul'. Ju Si-gyeong devoted himself to
educating and studying Korean language and letters with great
affection for them. He began to use terms such as 'Hannarageul(한나라글),
Hannaramal(한나라말), Hanmal(한말)', and he changed
the names of 'Baedalmalgeul Modeum(배달말글 몯음)' or
'Joseoneo Gangseupwon(조선어 강습원)' to 'Hangeul mo(한글모)',
'Hangeulbaegot(한글배곧)', and he also wrote 'Hangeul Puri(한글풀이)' for
the children's magazine 'Aidle Boy(아이들보이)'(1913. 9) The name
'Hangeul' was generalized since then.