I suggest adding a possibility to provide a description for each custom field.
That would allow to provide hints in the UI on how to fill the fields properly.
For example
Field name
Field Description
Word
English word
IPA
International Phonetic Transcription for all possible pronunciations, separated by semicolons
Meaning
Meaning of the word in this example
Example
Example sentence or phrase
Synonyms
Word's synonyms that could be used in the same example
Register
i.e. formal, informal, vulgar, legal, etc. (comma-separated list)
Image
word's image file (picture), applicable to this example
Heterographs
words that sound the same, but have different meaning and spelling (comma-separated list)
How would you like these descriptions to be represented in the UI? My first thought would be a tooltip that is shown when hovering the field name (or an info icon like in the new deck options)…