Here's one way to approach this problem:

1. Iterate through each word in the dictionary.
2. For each word, check if it is a subsequence of the input string.
3. If it is a subsequence, check if it is longer than the current longest subsequence found so far.
4. If it is longer, update the current longest subsequence found.

Here's some sample code that implements this approach:

```
def find_longest_subsequence(input_string, dictionary):
    longest_subsequence = ""
    
    for word in dictionary:
        i, j = 0, 0
        while i < len(input_string) and j < len(word):
            if input_string[i] == word[j]:
                j += 1
            i += 1
        if j == len(word) and len(word) > len(longest_subsequence):
            longest_subsequence = word
                
    return longest_subsequence
```

Using the input string "abpppl" and dictionary ["able", "apple", "sample", "abppl", "pl"], this function would return "apple" as the longest word in the dictionary that is a subsequence of the input string.
Input string: abpppl
Dictionary: [able, apple, sample, abppl, pl]
Data una stringa di input e un dizionario, crea una funzione trova la parola più lunga nel dizionario che è una sottosequenza della stringa data.