Using strcpy to copy elements of an char array to another array

So I building a spell checker and I have this as my TrieNode class:

class TrieNode{
public:
    bool isWord;
    char word[100][20];
    TrieNode* letter[alphabetSize];

I have an insert method inside my Trie class which is:

    void insert(TrieNode* root, char* wordInsert);

I was able to insert the letters of char* word into my trie

This is what I have for my insert function:

void Trie::insert(TrieNode* root, char* wordInsert) {
    TrieNode* currentNode = root;
    int wordLength = strlen(wordInsert);
    for (int i = 0; i < wordLength; i++) {
        //strcpy(currentNode->word[i], currentNode->letter);
        int index = wordInsert[i]- 'a';
        if(!currentNode->letter[index]){
            currentNode->letter[index] = new TrieNode();
        }
        currentNode = currentNode->letter[index];
    }
    currentNode->isWord = true;

}

Now I want to insert the current->letter[i] into my other char* array in my TrieNode class called word

I tried doing

strcpy(currentNode->word, currentNode->letter[i])

but I get an error saying :

No matching function for call to 'strcpy'

How would I be able to get the elements from the letter array into the array called word which is also in my TrieNode class